Fast gas switching plasma processing apparatus

ABSTRACT

A plasma chamber with a plasma confinement zone with an electrode is provided. A gas distribution system for providing a first gas and a second gas is connected to the plasma chamber, wherein the gas distribution system can substantially replace one gas in the plasma zone with the other gas within a period of less than 1 s. A first frequency tuned RF power source for providing power to the electrode in a first frequency range is electrically connected to the at least one electrode wherein the first frequency tuned RF power source is able to minimize a reflected RF power. A second frequency tuned RF power source for providing power to the plasma chamber in a second frequency range outside of the first frequency range wherein the second frequency tuned RF power source is able to minimize a reflected RF power.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/601,293 filed on Nov. 17, 2006, which is a Continuation-In-Part ofU.S. application Ser. No. 10/835,175 filed on Apr. 30, 2004, now U.S.Pat. No. 7,708,859, issued on May 4, 2010, entitled “GAS DISTRIBUTIONSSYSTEM HAVING FAST GAS SWITCHING CAPABILITIES”, which are herebyincorporated by reference in their entirety.

BACKGROUND

Semiconductor structures are processed in plasma processing apparatusesincluding a plasma processing chamber, a gas source that suppliesprocess gas into the chamber, and an energy source that produces plasmafrom the process gas. Semiconductor structures are processed in suchapparatuses by techniques including dry etching processes, depositionprocesses, such as chemical vapor deposition (CVD), physical vapordeposition, or plasma-enhanced chemical vapor deposition (PECVD) ofmetal, dielectric and semiconductor materials and resist strippingprocesses. Different process gases are used for these processingtechniques, as well as processing different materials of semiconductorstructures.

SUMMARY

To achieve the foregoing and in accordance with the purpose of thepresent invention, a plasma wafer processing tool is provided. A plasmachamber with a plasma confinement zone with a volume and at least oneelectrode is provided. A gas distribution system for providing a firstgas and a second gas is connected to the plasma chamber, wherein the gasdistribution system can substantially replace one of the first gas andthe second gas in the plasma zone with the other of the first gas andthe second gas within a period of less than 1 s, wherein a first plasmaformed in the plasma zone from the first gas provides a first impedanceload and wherein a second plasma formed in the plasma zone from thesecond gas provides a second impedance load different than the firstimpedance load. A first frequency tuned RF power source for providingpower to the at least one electrode in a first frequency range iselectrically connected to the at least one electrode wherein the firstfrequency tuned RF power source is able to receive reflected RF powerand tune an output RF frequency to minimize the reflected RF power. Asecond frequency tuned RF power source for providing power to the plasmachamber in a second frequency range outside of the first frequency rangewherein the second frequency tuned RF power source is able to receivereflected RF power and tune an output RF frequency to minimize thereflected RF power.

In another manifestation of the invention a plasma processing apparatusis provided. A plasma processing chamber including a showerheadelectrode assembly having the inner and outer zones and an interiorvolume of about ½ liter to 4 liters is provided. A gas distributionsystem is in fluid communication with the inner and outer zones of theshowerhead electrode assembly, wherein the gas distribution system isoperable to substantially replace a first process gas or a secondprocess gas in the plasma confinement zone with the other of the firstprocess gas or the second process gas within a period of less than about1 s. The gas distribution comprises a gas supply system, which providesthe first process gas and the second process gas, a flow control systemin fluid communication with the gas supply system, which splits a flowof the first process gas into an inner zone flow of the first processgas and an outer zone flow of the first process gas and which splits aflow of the second process gas into an inner zone flow of the secondprocess gas and an outer zone flow of the second process gas, and aswitching section, which is in fluid connection between the flow controlsystem and the inner zone and outer zone of the gas distribution member,wherein the switching section switches flow to the inner zone of the gasdistribution member between the inner zone flow of the first process gasand the inner zone of the second process gas and wherein the switchingsection switches flow to the outer zone of the gas distribution memberbetween the outer zone flow of the first process gas and the outer zoneflow of the second process gas. A first frequency tuned RF power sourcefor provides power to the plasma processing apparatus in a firstfrequency range wherein the first frequency tuned RF power source isable to receive reflected RF power and tune an output RF frequency tominimize the reflected RF power. A second frequency tuned RF powersource for provides power to the plasma processing apparatus in a secondfrequency range outside of the first frequency range wherein the secondfrequency tuned RF power source is able to receive reflected RF powerand tune an output RF frequency to minimize the reflected RF power.

In another manifestation of the invention, a method of processing asemiconductor structure in a plasma processing chamber is provided. a) Afirst process gas is supplied into the plasma processing chamber whilediverting a second process gas to a bypass-line, the plasma processingchamber containing a semiconductor substrate including at least onelayer and a patterned resist mask overlying the layer. b) The firstprocess gas is energized to produce a first plasma with a firstimpedance load and (i) etching at least one feature in the layer or (ii)forming a polymer deposit on the mask. c) A first RF power source isfrequency tuned to a first frequency to match the first impedance load.d) A second RF power source is frequency tuned to a second frequencydifferent than the first frequency to match the first impedance load. e)The flows of the first and second process gases are switched so that thesecond process gas is supplied into the plasma processing chamber whilediverting the first process gas to the by-pass line, the first processgas being substantially replaced in a plasma confinement zone of theplasma processing chamber by the second process gas within a period ofless than about 1 s. f) The second process gas is energized to produce asecond plasma with a second impedance load different from the firstimpedance load and (iii) etching the at least one feature in the layeror (iv) forming a polymer deposit on the layer and the mask. g) Thefirst RF power source is frequency tuned to a third frequency differentthan the first and second frequencies to match the second impedanceload. h) The second RF power source is frequency tuned to a fourthfrequency different than the first, second, and third frequencies tomatch the second impedance load. i) The flows of the first and secondprocess gases are switched so that the first process gas is suppliedinto the plasma processing chamber while diverting the second processgas to the by-pass line, the second process gas being substantiallyreplaced in the plasma confinement zone of the plasma processing chamberby the first process gas within a period of less than about 1 s. j)Steps b)-i) are repeated a plurality of times with the substrate.

These and other features of the present invention will be described inmore details below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a sectional view of an exemplary embodiment of a plasmaprocessing apparatus that preferred embodiments of the gas distributionsystem can be used with.

FIG. 2 illustrates a preferred embodiment of the gas distributionsystem.

FIG. 3 depicts a preferred embodiment of a gas supply section of the gasdistribution system.

FIG. 4 depicts a preferred embodiment of a flow control section of thegas distribution system.

FIG. 5 depicts a first preferred embodiment of a gas switching sectionof the gas distribution system.

FIG. 6 depicts a second preferred embodiment of the gas switchingsection of the gas distribution system.

FIG. 7 depicts a third preferred embodiment of the gas switching sectionof the gas distribution system.

DETAILED DESCRIPTION

Plasma processing apparatuses for processing semiconductor materials,such as semiconductor devices formed on semiconductor substrates, e.g.,silicon wafers, include a plasma processing chamber and a gasdistribution system that supplies process gas into the plasma processingchamber. The gas distribution system can distribute gas to a single zoneor multiple zones across the surface of a substrate during plasmaprocessing. The gas distribution system can include flow controllers tocontrol the flow ratio of the same or different process gas, or gasmixture, to the zones, thereby allowing in-process adjustment ofacross-substrate uniformity of gas flow and gas composition.

Although multiple-zone gas distribution systems can provide improvedflow control as compared to a single-zone system, it may be desirable toprovide such systems with an arrangement that allows substrateprocessing operations in which the gas composition and/or the gas flowcan be changed within a short period of time.

A gas distribution system is provided for supplying different gascompositions and/or flow ratios to a chamber. In a preferred embodiment,the gas distribution system is adapted to be in fluid communication withan interior of a vacuum chamber, such as a plasma processing chamber ofa plasma processing apparatus, and provide the capability of supplyingdifferent gas chemistries and/or gas flow rates to the vacuum chamberduring processing operations. The plasma processing apparatus can be alow-density, medium-density or high-density plasma reactor including anenergy source that uses RF energy, microwave energy, magnetic fields, orthe like to produce plasma. For example, the high-density plasma can beproduced in a transformer coupled plasma (TCP™) reactor, also known asan inductively coupled plasma reactor, an electron-cyclotron resonance(ECR) plasma reactor, a capacitive-type discharge, or the like.Exemplary plasma reactors that preferred embodiments of the gasdistribution system can be used with include Exelan™ plasma reactors,such as the 2300 Excelan™ plasma reactor, available from Lam ResearchCorporation, located in Fremont, Calif. During plasma etching processes,multiple frequencies can be applied to a substrate support incorporatingan electrode and an electrostatic chuck. Alternatively, indual-frequency plasma reactors, different frequencies can be applied tothe substrate support and an electrode, such as a showerhead electrode,spaced from the substrate.

A preferred embodiment of the gas distribution system can supply a firstgas into the interior of a vacuum chamber, such as a plasma processingchamber, via a single zone or multiple zones, preferably at least aninner zone and an outer zone of a gas distribution member adjacent to anexposed surface of a substrate to be processed. The inner and outerzones are radially spaced, and preferably, flow insulated, from eachother in the plasma processing chamber. The gas distribution system cansimultaneously divert a second gas that is different from the first gasto a vacuum chamber by-pass line. The by-pass line can be in fluidcommunication with a vacuum pump, or the like. In a preferredembodiment, the first gas is a first process gas and the second gas is adifferent process gas. For example, the first gas can be a first etchgas chemistry or deposition gas chemistry, and the second gas can be adifferent etch gas chemistry or deposition gas chemistry. The gasdistribution system can simultaneously provide different controlled flowrates of the first gas to the inner zone and the outer zone,respectively, while the second gas is diverted to the by-pass line, andvice versa. By diverting one of the gases to the by-pass line, changeover of the gas supplied to the vacuum chamber can be achieved within ashort period of time.

The gas distribution system includes switching devices that allow gasswitching, or gas change over, in a short period of time between firstand second gases supplied to an interior of a vacuum chamber thatincludes a single zone or includes multiple zones. For multiple-zonesystems, the gas distribution system can supply the first gas to theinner zone and outer zone while the second gas is diverted to theby-pass line, and then switch the gas distributions within a shortperiod of time so that the second gas is supplied to the inner zone andouter zone while the first gas is diverted to the by-pass line. The gasdistribution system can alternately supply the first and second gasesinto the interior of the vacuum chamber, each for a desired period oftime to allow quick change over between different processing operationsthat use different gas chemistries, e.g., alternating steps of a methodof processing a semiconductor device. In a preferred embodiment, themethod steps can be different etch steps, e.g., a faster etch step, suchas a main etch, and a relatively slower etch step, such as an over etchstep; an etch step and a material deposition step; or different materialdeposition steps that deposit different materials onto a substrate.

In a preferred embodiment of the gas distribution system, a volume of agas composition in a confined region within a vacuum chamber, preferablya plasma confinement zone, can be replaced (i.e., flushed out) byanother gas composition introduced into the vacuum chamber within ashort period of time. Such gas replacement preferably can be achieved inless than about 1 s, more preferably within less than about 200 ms, byproviding valves having a fast switching capability in the gasdistribution system. The plasma confinement zone can have a gas volumeof about ½ liter to about 4 liters for a plasma processing chamber forprocessing 200 mm or 300 mm wafers. The plasma confinement zone can bedefined by a stack of confinement rings, such as disclosed incommonly-owned U.S. Pat. No. 5,534,751, which is hereby incorporated byreference in its entirety.

FIG. 1 depicts an exemplary semiconductor material plasma processingapparatus 10 that embodiments of the gas distribution system 100 can beused with. The apparatus 10 comprises a vacuum chamber or plasmaprocessing chamber 12 having an interior containing a substrate support14 on which a substrate 16 is supported during plasma processing. Thesubstrate support 14 includes a clamping device, preferably anelectrostatic chuck 18, which is operable to clamp the substrate 16 onthe substrate support 14 during processing. The substrate can besurrounded by focus rings and/or edge rings, ground extensions or otherparts, such as parts disclosed in commonly-owned U.S. Patent ApplicationPublication No. US 2003/0029567, which is incorporated herein byreference in its entirety.

In a preferred embodiment, the plasma processing chamber 12 includes aplasma confinement zone having a volume of about ½ liter to about 4liters, preferably about 1 liter to about 3 liters. For example, theplasma processing chamber 12 can include a confinement ring arrangement,such as disclosed in commonly-owned U.S. Pat. No. 5,534,751, which isincorporated herein by reference in its entirety, to define the plasmaconfinement zone. The gas distribution system can replace such a volumeof gas in the plasma confinement zone with another gas within a periodof less than about 1 s, preferably in less than about 200 ms, withoutsubstantial back diffusion. A confinement mechanism, such as confinementrings 120, can limit the fluid communication from the plasma volume toportions of the interior of the plasma processing chamber 12 that areoutside of the plasma volume.

The substrate 16 may include a base material, such as a silicon wafer;an intermediate layer of a material that is to be processed, e.g.,etched, over the base material; and a masking layer over theintermediate layer. The intermediate layer may be of a conductive,dielectric, or semiconductive material. The masking layer can bepatterned photoresist material having an opening pattern for etchingdesired features, e.g., holes, vias and/or trenches, in the intermediatelayer and/or one or more other layers. The substrate can includeadditional layers of conductive, dielectric or semiconductive materialsbetween the base layer and the masking layer, depending on the type ofsemiconductor device formed on the base material.

Exemplary dielectric materials that can be processed are, for example,doped silicon oxide, such as fluorinated silicon oxide; un-doped siliconoxide, such as silicon dioxide; spin-on glass; silicate glasses; dopedor un-doped thermal silicon oxide; and doped or un-doped TEOS depositedsilicon oxide. Such dielectric materials can overlie a conductive orsemiconductive layer, such as polycrystalline silicon; metals, such asaluminum, copper, titanium, tungsten, molybdenum and their alloys;nitrides, such as titanium nitride; and metal silicides, such astitanium silicide, tungsten silicide and molybdenum silicide.

The exemplary plasma processing apparatus 10 shown in FIG. 1 includes ashowerhead electrode assembly having a support plate 20 forming a wallof the plasma chamber, and a showerhead 22 attached to the supportplate. A baffle assembly is located between the showerhead 22 and thesupport plate 20 to uniformly distribute process gas to a backside 28 ofthe showerhead. The baffle assembly can include one or more baffleplates. In the embodiment, the baffle assembly includes baffle plates30A, 30B, and 30C. Open plenums 48A, 48B and 48C are defined between thebaffle plates 30A, 30B and 30C; and between the baffle plate 30C andshowerhead 22. The baffle plates 30A, 30B and 30C and showerhead 22include through passages for flowing process gas into the interior ofplasma processing chamber 12.

A first frequency tuned RF power source 104 is controllably connected toa controller 500 and provides power to the showerhead electrode 22through a first mechanical match box 106. The first frequency tuned RFpower source 104 provides a variable frequency, which in this embodimentranges from 1.7 MHz to 2.2 MHz, so that 2 MHz lies within the variablefrequency range The first frequency tuned RF power source is formed toreceive and measure output power and reflected RF power and to vary thefrequency in the frequency range of 1.7 MHz to 2.2 MHz to minimizereflected RF power from the first frequency tuned RF power source 104.

A second frequency tuned RF power source 108 is controllably connectedto a controller 500 and provides power to the showerhead electrode 22through a second mechanical match box 110. The second frequency tuned RFpower source 108 provides a variable frequency, which in this embodimentranges from 26.7 MHz to 27.2 MHz, so that 27 MHz lies within thevariable frequency range. The second frequency tuned RF power source isformed to receive and measure output power and reflected RF power and tovary the frequency in the frequency range of 26.7 MHz to 27.2 MHz tominimize reflected RF power from the second frequency tuned RF powersource 108.

A third frequency tuned RF power source 112 is controllably connected toa controller 500 and provides power to the showerhead electrode 22through a third mechanical match box 114. The third frequency tuned RFpower source 112 provides a variable frequency, which in this embodimentranges from 59.7 MHz to 60.2 MHz, so that 60 MHz lies within thevariable frequency range. The third frequency tuned RF power source 112is formed to receive and measure output power and reflected RF power andto vary the frequency in the frequency range of 59.7 MHz to 60.2 MHz tominimize reflected RF power from the third frequency tuned RF powersource 112.

In this example, the first, second, and third frequency tuned RF powersources vary the frequency over a range of 0.5 MHz to provide RF tuning.In other embodiments, the frequency tuned RF power sources vary thefrequency over a range of less than 2 MHz. More preferably, thefrequency tuned RF power sources vary the frequency over a range of lessthan 1 MHz. The tuning range should be large enough to minimizereflected power and yet small enough to allow fast tuning.

In the embodiment, the plenum between the plate 20 and the baffle plate30A and the plenums 48A, 48B and 48C between the baffle plates 30A, 30Band 30C are divided into an inner zone 42 and an outer zone 46 by seals38 a, 38 b, 38 c and 38 d, such as O-rings. The inner zone 42 and outerzone 46 can be supplied process gas having different respective gaschemistries and/or flow rates by the gas distribution system 100,preferably under control of the controller 500. Gas is supplied from aninner zone gas supply 40 into the inner zone 42, and gas is suppliedfrom an outer zone gas supply 44 into an annular channel 44 a and theninto the outer zone 46. The process gas flows through the passages inthe baffle plates 30A, 30B and 30C and the showerhead 22 and into theinterior of the plasma processing chamber 12.

In other preferred embodiments, the plasma processing apparatus 10 caninclude a gas injector system for injecting process gas into the plasmaprocessing chamber. For example, the gas injector system can have aconfiguration as disclosed in commonly-owned U.S. patent applicationSer. No. 09/788,365, U.S. patent application Ser. No. 10/024,208, U.S.Pat. No. 6,013,155, or U.S. Pat. No. 6,270,862, each of which isincorporated herein by reference in its entirety.

The process gas is energized into the plasma state in the plasmaprocessing chamber 12 by a power source, such as an RF source drivingelectrode 22, or a power source driving an electrode in the substratesupport 14. The RF power applied to the electrode 22 can be varied whendifferent gas compositions are supplied into the plasma processingchamber 12, preferably within a time period of less than about 1 s, morepreferably less than about 200 ms. The change in gas compositions canchange the load or impedance from the gas. The first, second, and thirdRF power sources 104, 108, 112 may have mechanical impedance matchingdevices, but such devices may not be fast enough to match the changingimpedance when different gas compositions are provided for time periodsless than about 1 s. Therefore, the first, second, and third RF powersources have variable frequencies and are able to measure output andreflected RF power and to vary the frequency to minimize reflected RFpower. The minimizing the reflected RF power matches the impedance ofthe load from the plasma in the processing chamber with the RF powersources through a matchbox.

FIG. 2 shows a preferred embodiment in which the gas distribution system100 includes a gas supply section 200, a flow control section 300, and agas switching section 400 in fluid communication with each other. Thegas distribution system 100 preferably also includes a controller 500(FIG. 1), which is connected in control communication to controloperation of the gas supply section 200, flow control section 300 andgas switching section 400.

In the gas distribution system 100, the gas supply section 200 cansupply different gases, such as first and second process gases, to theflow control section 300 via respective first and second gas lines 235,245. The first and second gases can have different compositions and/orgas flow rates from each other.

The flow control section 300 is operable to control the flow rate, andoptionally also to adjust the composition, of different gases that canbe supplied to the switching section 400. The flow control section 300can provide different flow rates and/or chemistries of the first andsecond gases to the switching section 400 via gas passages 324, 326 and364, 366, respectively. In addition, the flow rate and/or chemistry ofthe first gas and/or second gas that is supplied to the plasmaprocessing chamber 12 (while the other gas is diverted to by-pass line50, which can be in fluid communication with a vacuum pumping system,such as between a turbo pump and a roughing pump) can be different forthe inner zone 42 and the outer zone 46. Accordingly, the flow controlsection 300 can provide desired gas flows and/or gas chemistries acrossthe substrate 16, thereby enhancing substrate processing uniformity.

In the gas distribution system 100, the switching section 400 isoperable to switch from the first gas to the second gas within a shortperiod of time to allow the first gas to be replaced by the second gasin a single zone or multiple zones, e.g., the inner zone 42 and theouter zone 46, while simultaneously diverting the first gas to theby-pass line, or vice versa. The gas switching section 400 preferablycan switch between the first and second gases without the occurrence ofundesirable pressure surges and flow instabilities in the flow of eithergas. If desired, the gas distribution system 100 can maintain asubstantially constant sequential volumetric flow rate of the first andsecond gases through the plasma processing chamber 12.

FIG. 3 shows a preferred embodiment of the gas supply section 200 of thegas distribution system 100. The gas supply section 200 is preferablyconnected to the controller 500 to control operation of flow controlcomponents, such as valves and flow controllers, to allow control of thecomposition of two or more gases that can be supplied by the gas supplysection 200. In the embodiment, the gas supply section 200 includesmultiple gas sources 202, 204, 206, 208, 210, 212, 214 and 216, eachbeing in fluid communication with the first gas line 235 and the secondgas line 245. As such, the gas supply section 200 can supply manydifferent desired gas mixtures to the plasma processing chamber 12. Thenumber of gas sources included in the gas distribution system 100 is notlimited to any particular number of gas sources, but preferably includesat least two different gas sources. For example, the gas supply section200 can include more than or less than the eight gas sources included inthe embodiment shown in FIG. 3. For example, the gas supply section 200can include two, three, four, five, ten, twelve, sixteen, or more gassources. The different gases that can be provided by the respective gassources include individual gases, such as O₂, Ar, H₂, Cl₂, N₂ and thelike, as well as gaseous fluorocarbon and/or fluorohydrocarboncompounds, such as CF₄, CH₃F and the like. In one preferred embodiment,the plasma processing chamber is an etch chamber and the gas sources202-216 can supply Ar, O₂, N₂, Cl₂, CH₃, CF₄, C₄F₈ and CH₃F or CHF₃ (inany suitable order thereof). The particular gases supplied by therespective gas sources 202-216 can be selected based on the desiredprocess that is to be performed in the plasma processing chamber 12,e.g., particular dry etching and/or material deposition processes. Thegas supply section 200 can provide broad versatility regarding thechoice of gases that can be supplied for performing etching processesand/or material deposition processes.

The gas supply section 200 preferably also includes at least one tuninggas source to adjust the gas composition. The tuning gas can be, e.g.,O₂, an inert gas, such as argon, or a reactive gas, such as afluorocarbon or fluorohydrocarbon gas, e.g., C₄F₈. In the embodimentshown in FIG. 3, the gas supply section 200 includes a first tuning gassource 218 and a second tuning gas source 219. As described below, thefirst tuning gas source 218 and second tuning gas source 219 can supplytuning gas to adjust the composition of the first and/or second gassupplied to the gas switching section 400.

In the embodiment of the gas supply section 200 shown in FIG. 3, a flowcontrol device 240 preferably is disposed in each of the gas passages222, 224, 226, 228, 230, 232, 234 and 236 in fluid communication withthe gas sources 202, 204, 206, 208, 210, 212, 214 and 216, respectively,and also in the gas passages 242, 244 in fluid communication with thefirst tuning gas source 218 and the second tuning gas source 219,respectively. The flow control devices 240 are operable to control theflow of the gas supplied by the associated gas sources 202-216 and 218,219. The flow control devices 240 preferably are mass flow controllers(MFCs).

In the embodiment shown in FIG. 3, valves 250, 252 are located along thegas passages downstream of each of the gas sources 202-216. The valves250, 252 can be selectively opened or closed, preferably under controlof the controller 500, to allow different gas mixtures to be flowed tothe first gas line 235 and/or the second gas line 245. For example, byopening the valves 252 associated with one or more of the gas sources202-216 (while the remaining valves 252 associated with the other onesof the gas sources 202-216 are closed), a first gas mixture can besupplied to the first gas line 235. Likewise, by opening the valves 250associated with one or more of the other gas sources 202-216 (while theremaining valves 250 associated with the other ones of the gas sources202-216 are closed), a second gas mixture can be supplied to the secondgas line 245. Accordingly, various mixtures and mass flow rates of thefirst and second gases can be provided to the first gas line 235 and thesecond gas line 245 by controlled operation of the gas supply section200.

In a preferred embodiment, the gas supply section 200 is operable toprovide a continuous flow of the first and second gases via the firstgas line 235 and the second gas line 245, respectively. The first gas orthe second gas is flowed to the plasma processing chamber 12 while theother gas is diverted to the by-pass line. The by-pass line can beconnected to a vacuum pump, or the like. By continuously flowing both ofthe first and second gases, the gas distribution system 100 can achieverapid change over of the gas flow.

FIG. 4 shows a preferred embodiment of the flow control section 300 ofthe gas distribution system 100. The flow control section 300 includes afirst flow control section 305 in fluid communication with the first gasline 235 from the gas supply section 200, and a second flow controlsection 315 in fluid communication with the second gas line 245 from thegas supply section 200. The flow control section 300 is operable tocontrol the ratio of the first gas supplied to the inner zone 42 andouter zone 46, respectively, while the second gas is diverted to theby-pass line, and to control the ratio of the second gas supplied to theinner zone 42 and outer zone 46, respectively, while the first gas isdiverted to the by-pass line. The first flow control section 305 dividesthe flow of the first gas introduced at the first gas line 235 into twoseparate outlet flows of the first gas, and the second flow controlsection 315 divides the flow of the second gas introduced at the secondgas line 245 into two separate outlet flows of the second gas. The firstflow control section 305 includes first and second gas passages 324, 326in fluid communication with the inner zone 42 and outer zone 46,respectively, via the switching system 400, and the second flow controlsection 315 includes first and second gas passages 364, 366 in fluidcommunication with the inner zone 42 and outer zone 46, respectively,via the switching system 400.

In a preferred arrangement, the first flow control section 305 and thesecond flow control section 315 each include at least two flowrestrictors. Each flow restrictor preferably has a fixed restrictionsize for gas flow through it. The flow restrictors are preferablyorifices. The flow restrictors restrict gas flow and maintain anapproximately constant gas pressure in a region of the gas passagesupstream of and proximate the orifices. Each of the first flow controlsection 305 and the second flow control section 315 preferably includesa network of orifices, e.g., two, three, four, five or more orifices,each preferably having a different cross-sectional restriction size,e.g., a different diameter or a different cross-sectional area. Therestriction sizes of the orifices are smaller than the cross-sectionalareas of the other portions of the gas flow path of the gas distributionsystem 100. The orifices are preferably sonic orifices. The gas flowsare preferably operated at the critical flow regime in the flow controlsection 300 so that the flow conductance of a given orifice isdetermined solely by its restriction size and upstream pressure. As theflow conductance of an orifice increases, the pressure drop across theorifice to achieve a given flow rate through the orifice decreases.

In the embodiment shown in FIG. 4, the first and second flow controlsections 305, 315 each include five orifices 330, 332, 334, 336 and 338.For example, the orifices 330, 332, 334, 336 and 338 can have relativerestriction sizes, e.g., diameters, of one, two, four, eight, andsixteen, respectively. Accordingly, when gas flow occurs through allfive orifices 330-338, the four orifices 330-336 have approximately thesame total conductance as that of the single orifice 338. Alternatively,up to three of the four orifices 330-336 can be opened to providedifferent ratios of the total conductance of the orifices 330-336 ascompared to the conductance of the orifice 338, in order to supplydifferent ratios of the first gas flow and the second gas flow to theinner zone 42 and the outer zone 46. Another embodiment can include adifferent number of orifices, e.g., a total of two orifices; includingthe orifice 338 and a second orifice that replaces the multiple orifices330-336. The second orifice preferably has the same restriction size asthe orifice 338. In such embodiment, the flow ratio of the first gasand/or second gas supplied to the inner zone 42 and the outer zone 46 isapproximately 1:1.

Valves 320 preferably are located upstream of each of the respectiveorifices 330-338 to control the flow of the first and second gases tothe orifices. For example, in the first flow control section 305 and/orthe second flow control section 315, one or more of the valves 320 canbe opened to allow flow of the first gas and/or second gas to one ormore of the associated orifice(s) 330-336, while the other valve 320 isopened to allow flow of the first gas and/or the second gas to theorifice(s) 338.

In the first flow control section 305, the orifices 330-336 are in fluidcommunication with the gas passage 322. The gas passage 322 is dividedinto the first and second gas passages 324, 326, which are in fluidcommunication with the gas switching section. A pair of valves 320 islocated in the first and second gas passages 324, 326 to control flow ofthe first gas flowed through one or more of the orifices 330-336 of thefirst flow control section 305 to the inner zone 42 and/or the outerzone 46. In an alternative embodiment, the pair of valves 320 locatedalong the gas passages 324, 326 can be replaced by a single, four-wayvalve.

In the first flow control section 305, the orifice 338 is arranged alongthe gas passage 319. The gas passage 319 is divided into gas passages331, 333, which are in fluid communication with the first and second gaspassages 324, 326, respectively. A pair of valves 320 is located in thegas passages 331, 333 to control flow of the first gas flowed throughthe orifice 338 to the first and second gas passages 324, 326. In analternative embodiment, the pair of valves 320 located along the gaspassages 331, 333 can be replaced by a single, four-way valve.

In the second flow control section 315, a pair of valves 320 is locatedalong the first and second gas passages 364, 366 to control flow of thesecond gas flowed through one or more of the orifices 330-336 to theinner zone 42 and the outer zone 46 of the plasma processing chamber. Inan alternative embodiment, the pair of valves 320 located along the gaspassages 364, 366 can be replaced by a single, four-way valve.

In the second flow control section 315, the orifice 338 is arrangedalong the gas passage 359. The gas passage 359 is divided into gaspassages 372, 374, which are in fluid communication with the first andsecond gas passages 364, 366, respectively. A pair of valves 320 islocated in the gas passages 372, 374 to control flow of the second gasflowed through the orifice 338 to the first and/or second gas passages364, 366. In an alternative embodiment, the pair of valves 320 locatedalong the gas passages 372, 374 can be replaced by a single four-wayvalve.

The orifices 330-338 are included in the flow control section 300 toprevent pressure surges and flow instabilities in the gas flow when thegas distribution system 100 changes the gas flowed into the plasmaprocessing chamber 12 from the first gas to the second gas, and viceversa.

In the embodiment shown in FIG. 4, the gas passage 242 of the firsttuning gas source 218 (FIG. 3) is arranged to supply the first tuninggas to the first gas passage 324 and/or second gas passage 326 of thefirst flow control section 305 to adjust the first gas composition. Thegas passage 244 of the second tuning gas source 219 (FIG. 3) is arrangedto supply the second tuning gas to the first gas passage 364 and/orsecond gas passage 366 of the second flow control section 315 to adjustthe second gas composition. The first and second tuning gases can be thesame tuning gas or different tuning gases.

A flow control device 340, preferably an MFC, is arranged along the gaspassage 242. Valves 320 are located along the gas passages 337, 339 tocontrol flow of the first tuning gas into the gas passage 326, 324,respectively. In an alternative embodiment, the pair of valves 320located along the gas passages 337, 339 can be replaced by a single,four-way valve.

A flow control device 340, preferably an MFC, is arranged along the gaspassage 244. Valves 320 are located along the gas passages 376, 378 tocontrol flow of the second tuning gas into the gas passages 366, 364,respectively. In an alternative embodiment, the pair of valves 320located along the gas passages 376, 378 can be replaced by a single,four-way valve.

In the embodiment of the flow control section 300 shown in FIG. 4, thefirst flow control section 305 and the second flow control section 315include the same components arranged in the same configuration. However,in other preferred embodiments of the gas distribution system 100, thefirst and second flow control sections 305, 315 can have differentcomponents and/or different configurations from each other. For example,the first and second flow control sections 305, 315 can includedifferent numbers of orifices and/or orifices with different restrictionsizes from each other.

In the gas distribution system 100, the gas switching system 400 is influid communication with the flow control section 300, and with theinterior of the vacuum chamber and the by-pass line to which the firstand second gases are flowed. A first preferred embodiment of the gasswitching system 400 is depicted in FIG. 5. The gas switching system 400can alternately supply first and second gases to both the inner zone 42and the outer zone 46 of the plasma processing chamber 12. The gasswitching system 400 is in fluid communication with the first gaspassage 324 and the second gas passage 326 of the first flow controlsection 305, and with the first gas passage 364 and the second gaspassage 366 of the second flow control section 315. An orifice 430 isarranged along each of the gas passages 324, 326, 364 and 366 to preventundesirable pressure surges during change over of the first and secondgases.

The first gas passage 324 of the first flow control section 305 isdivided into gas passages 448, 450; the second gas passage 326 of thefirst flow control section 305 is divided into gas passages 442, 444;the first gas passage 364 of the second flow control section 315 isdivided into gas passages 452, 454; and the second gas passage 366 ofthe second flow control section 315 is divided into gas passages 456,458. In the embodiment, the gas passage 442 is in fluid communicationwith the outer zone 46 of the plasma chamber 12, the gas passage 448 isin fluid communication with the inner zone 42 of the plasma processingchamber 12, and the gas passage 444 provides a by-pass line. The gaspassage 456 is in fluid communication with the gas passage 442 to theouter zone 46. The gas passage 452 is in fluid communication with thegas passage 448 to the inner zone 42. The gas passages 450, 454 and 458are in fluid communication with the gas passage 444 to the by-pass line.

A valve 440 is arranged along each of the gas passages 442, 444, 448,450, 452, 454, 456, and 458. In an alternative embodiment, each of thepairs of valves 440 located along the gas passages 442, 444; 448, 450;452, 454; and 456, 458 can be replaced by a single, four-way valve. Thevalves 440 can be selectively opened and closed, preferably undercontrol of the controller 500, to supply the first or second gas to thechamber, while simultaneously diverting the other gas to the by-passline.

For example, to supply the first gas to the inner zone 42 and the outerzone 46 of the plasma processing chamber 12 and divert the second gas tothe by-pass line, the valves 440 along the gas passages 442, 448 and454, 458 are opened, while the valves 440 along the gas passages 444,450 and 452, 456 are closed. To switch the gas flow so that the secondgas is supplied to the inner zone 42 and the outer zone 46 of the plasmaprocessing chamber 12, while the first gas is diverted to the by-passline, the valves 440 along the gas passages 444, 450 and 452, 456 areopened, while the valves 440 along the gas passages 442, 448 and 454,458 are closed. In other words, a first group of valves 440 is openedand a second group of valves 440 is closed to supply the first gas tothe plasma processing chamber 12, and then the same first group ofvalves is closed and the same second group of valves 440 is opened tochange the gas flow to supply the second gas to the plasma processingchamber.

In the gas switching system 400, the valves 440 are fast-switchingvalves. As used herein, the term “fast-switching valve” means a valvethat can be opened or closed within a short period of time, preferablyless than about 100 ms, more preferably less than about 50 ms, afterreceiving a signal from the controller 500 to open or close. The valves440 are preferably electronically controlled and actuated by receiving asignal from the controller 500 to open or close. A suitable“fast-switching valve” that can be used in the gas switching system 400is valve model number FSR-SD-71-6.35, available from Fujikin of America,located in Santa Clara, Calif.

Accordingly, the gas switching system 400 can supply the first gas,e.g., to the interior of the vacuum chamber while diverting the secondgas to the by-pass line, and then, preferably under control of thecontroller 500, quickly switch these gas flows and supply the second gasto the vacuum chamber while diverting the first gas to the by-pass line.The amount of time that the first gas or second gas is supplied to thevacuum chamber before the gases are switched can be controlled by thecontroller 500. The volume of the gas passages 324, 326, 364, and 366between the associated orifices 430 and the valves 440 preferably isless than about 10 cm³. As explained above, the gas distribution systemcan be used with a plasma processing chamber including a plasmaconfinement zone to replace a gas volume of about ½ liter to about 4liters within a period of less than about 1 s, more preferably less thanabout 200 ms, to thereby stabilize the system.

A gas switching system 1400 according to a second preferred embodimentis depicted in FIG. 6. In the gas switching system 1400, a valve 440 andan orifice 430, which is located downstream of the valve 440 arearranged along each of the gas passages 442-458. Otherwise, the gasswitching system 1400 can have the same configuration as the gasswitching system 400. The orifices 430 prevent undesirable pressuresurges during switching of gases. In an alternative embodiment, each ofthe pairs of valves 440 located along the gas passages 442, 444; 448,450; 452, 454; and 456, 458 can be replaced by a single, four-way valve.

A gas switching system 2400 according to a third preferred embodiment isdepicted in FIG. 7. In this embodiment, the gas switching system 2400 isin fluid communication with a first gas passage 405 and a second gaspassage 415. The first and second gas passages 405, 415 can be, e.g., afirst gas outlet and a second gas outlet, respectively, of a flowcontrol section that, unlike the flow control section 300 shown in FIG.4, does not include both inner and outer zone gas outlets. An orifice430 is located along each of the first gas passage 405 and second gaspassage 415. The first gas passage 405 is divided into gas passages 422,424, and the second gas passage 445 is divided into gas passages 426,428. The gas passages 422 and 426 are in fluid communication with aninterior of a vacuum chamber, and the gas passages 424 and 428 are influid communication with a by-pass line. A valve 440 is located alongeach of the gas passages 422, 424 and 426, 428. In an alternativeembodiment, each of the pairs of valves 440 located along the gaspassages 422, 424; and 426, 428 can be replaced by a single, four-wayvalve.

For example, to supply the first gas to the vacuum chamber andsimultaneously route the second gas to the by-pass line, the valves 440along the fluid passages 422 and 428 are opened and the valves 440 alongthe gas passages 424 and 426 are closed. To switch the gas flows so thatthe second gas is supplied to the vacuum chamber and the first gas isdiverted to the by-pass line, the valves 440 along the fluid passages424 and 426 are opened and the valves 440 along the fluid passages 422and 428 are closed.

In another preferred embodiment of the gas switching system, theembodiment shown in FIG. 7 can be modified by removing the orifices 430arranged in the first gas passage 405 and second gas passage 415upstream of the valves 440, and instead arranging a orifice in each ofthe gas passages 422, 424, 426 and 428 downstream of the associatedvalves 440.

Preferred embodiments of the gas distribution system 100 can be used tosupply different gas chemistries and/or flow rates to the plasmaprocessing chamber 12 to perform various etching and/or depositionprocesses. For example, the gas distribution system 100 can supplyprocess gases to a plasma processing chamber to etch features in asilicon oxide, such as an SiO₂ layer protected by an overlying mask,such as a UV resist mask. The SiO₂ layer can be formed on asemiconductor wafer, such as a silicon wafer, having a diameter of 200mm or 300 mm. The features can be, e.g., vias and/or trenches. Duringsuch etching processes, it is desirable to deposit a polymer on portionsof the mask to repair striations, e.g., cracks or fissures, in the mask(i.e., to fill the striations) so that features etched in the SiO₂ havetheir desired shape, e.g., vias have a round cross-section. Ifstriations are not repaired, they can eventually reach the layerunderlying the mask and in effect be transferred to that layer duringetching. Also, a polymer can be deposited on the sidewalls of thefeatures.

It has been determined, however, that the thickness of the polymerdeposited on the sidewalls and the base of etched features affects theetch rate. In anisotropic etching processes, polymer deposited on thebottom of the feature is substantially removed during etching. However,if the polymer becomes too thick on the sidewalls and/or on the base,the etch rate of SiO₂ is decreased, and may be stopped completely.Polymer may also flake off of surfaces if it becomes too thick.Accordingly, the amount of time that the gas mixture for forming thepolymer deposit on the mask and features is supplied into the plasmaprocessing chamber is preferably controlled to thereby control thethickness of the polymer deposit formed on the SiO₂ layer, while alsoproviding sufficient repair and protection of the mask. During etchingof the SiO₂ layer, polymer is periodically removed from the mask.Accordingly, the polymer is preferably deposited on the mask betweenperiods of etching of the SiO₂ layer to ensure that sufficient repairand protection of the mask is achieved.

The gas distribution system 100 can be used to supply process gas into aplasma processing chamber to etch SiO₂ protected by an overlying mask,e.g., a UV resist mask, with control of the thickness of polymerdeposited on the features, and with repair and protection of the mask.The gas switching system of the gas distribution system 100 is operableto allow a first process gas used to etch the SiO₂ to be supplied intothe plasma processing chamber for a first period of time while a secondgas mixture used to form the polymer deposit is diverted to a bypassline, and then to quickly switch the gas flows so that the second gasmixture is supplied into the plasma processing chamber to form thepolymer deposit while the first gas mixture is supplied to the by-passline. Preferably, the first gas mixture supplied to a plasma confinementzone of the plasma processing chamber is at least substantially replacedwith the second gas mixture within a period of less than about 1 s, morepreferably less than about 200 ms. The plasma confinement zonepreferably has a volume of about ½ liter to about 4 liters.

The first gas mixture used to etch SiO₂ can contain, e.g., afluorocarbon species, such as C₄F₈, O₂, and argon. The flow ratio ofC₄F₈/O₂/argon can be, e.g., 20/10/500 sccm. Power is provided with at acombination of frequencies of 60 MHz, 27 MHz, and 2 MHz, at powers thatcan range from 50 to 5000 W. The second gas mixture used to form apolymer deposit can contain, e.g., a fluorohydrocarbon species, such asCH₃F, and argon. The flow ratio of CH₃F/argon can be, e.g., 15/500 sccm.The second gas mixture can optionally also include O₂. Power is providedat a combination of frequencies of 60 MHz, 27 MHz, and 2 MHz at powersthat can range from 50 to 5000 W. For a capacitive-coupled plasma etchreactor for processing 200 mm or 300 mm wafers, the chamber pressure canbe, e.g., 70-90 mTorr. The first gas mixture is preferably flowed intothe plasma processing chamber for about 5 seconds to about 20 secondseach time it is introduced into the chamber (while the second gas isdiverted to the by-pass line), and the second gas mixture is preferablyflowed into the plasma processing chamber for about 1 second to about 3seconds each time it is introduced into the chamber (while the first gasis diverted to the by-pass line). During etching of SiO₂ on a substrate,the length of the etching period and/or the polymer deposition periodcan be increased or decreased within the preferred time periods. Thepolymer deposit preferably reaches a maximum thickness of less thanabout 100 angstroms during the etching process, which typically lasts upto about 3 minutes. During etching, polymer can be deposited on the maskto repair striations and provide mask protection. Accordingly, the shapeof the openings in the mask preferably can be maintained during theetching process.

The first, second, and third mechanical match boxes 106, 110, 114 areused to provide gross impedance matching between the first, second, andthird frequency tuned RF power sources 104, 108, 112 and the load in theplasma processing chamber 12. The first, second, and third mechanicalboxes 106, 110, 114 are not able to precisely match the quickly changingimpedance load caused by the quickly changing recipe. Therefore, theinvention uses frequency tuning provided by the first, second, and thirdfrequency tuned RF power sources 104, 108, 112 to quickly and preciselymatch the quickly varying impedance of the load and the first, second,and third mechanical match boxes 106, 110, 114 with the impedance of thefirst, second, and third frequency tuned RF power sources 104, 108, 112.

Since the plasma conditions have to switch very rapidly betweendeposition and shaping (etch), there are several hardware features whichhave to work together. The gas volume must be small to reduce gastransition time in the processing chamber. This is achieved by makingthe plasma volume as small as possible using confinement rings. Also,the RF generators have to be able to rapidly tune in to the rapidlyvarying plasma conditions. This is achieved by using electronicallyfrequency tuned generators rather than conventional mechanical matchunits. For best critical dimension control (CD) and uniformity controlmain gases are split and the ratio of center to edge gas flows areselectable. Finally, a tuning gas is needed which can be the same ordifferent from the main gases and can be fed in a selectable flow to theedge or center of the wafer. So, combination of all the aforementionedhardware constitutes the overall performance desired for appliedprocesses put forth in this document.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and substituteequivalents, which fall within the scope of this invention. It shouldalso be noted that there are many alternative ways of implementing themethods and apparatuses of the present invention. It is thereforeintended that the following appended claims be interpreted as includingall such alterations, permutations, and substitute equivalents as fallwithin the true spirit and scope of the present invention.

1. A method of processing a semiconductor structure in a plasmaprocessing chamber, comprising: a) supplying a first process gas intothe plasma processing chamber while diverting a second process gas to abypass-line, the plasma processing chamber containing a semiconductorsubstrate including at least one layer and a patterned resist maskoverlying the layer; b) energizing the first process gas to produce afirst plasma with a first impedance load and (i) etching at least onefeature in the layer or (ii) forming a polymer deposit on the mask; c)frequency tuning a first RF power source to a first frequency to matchthe first impedance load; d) frequency tuning a second RF power sourceto a second frequency different than the first frequency to match thefirst impedance load; e) switching the flows of the first and secondprocess gases so that the second process gas is supplied into the plasmaprocessing chamber while diverting the first process gas to the by-passline, the first process gas being substantially replaced in a plasmaconfinement zone of the plasma processing chamber by the second processgas within a period of less than about 1 s; f) energizing the secondprocess gas to produce a second plasma with a second impedance loaddifferent from the first impedance load and (iii) etching the at leastone feature in the layer or (iv) forming a polymer deposit on the layerand the mask; g) frequency tuning the first RF power source to a thirdfrequency different than the first and second frequencies to match thesecond impedance load; h) frequency tuning the second RF power source toa fourth frequency different than the first, second, and thirdfrequencies to match the second impedance load; i) switching the flowsof the first and second process gases so that the first process gas issupplied into the plasma processing chamber while diverting the secondprocess gas to the by-pass line, the second process gas beingsubstantially replaced in the plasma confinement zone of the plasmaprocessing chamber by the first process gas within a period of less thanabout 1 s; and j) repeating b)-i) a plurality of times with thesubstrate.
 2. The method, as recited in claim 1, wherein the periods ofless than about 1 s is less than 200 ms.
 3. The method, as recited inclaim 1, wherein the polymer deposit is formed to a maximum thickness ofless than about 100 angstroms after repeating a)-i) a plurality of timeswith the substrate.
 4. The method, as recited in claim 1, furthercomprising: splitting a flow of the first process gas into an inner zoneflow and an outer zone flow, wherein the supplying the first process gasinto the plasma processing chamber provides the inner zone flow to aninner zone of the processing chamber and the outer zone flow to an outerzone of the processing chamber.
 5. The method, as recited in claim 4,further comprising providing a tuning gas to at least one of the innerzone flow of the first process gas and the outer zone flow of the firstprocess gas, wherein the tuning gas is provided after the splitting ofthe flow of the first process gas.
 6. The method of claim 5, wherein thefirst plasma etches the at least one feature in the layer, and thesecond plasma forms the deposit on the layer and the mask, the depositrepairing striations in the mask.
 7. The method of claim 1, wherein theplasma confinement zone has a volume of about ½ liter to about 4 liters.8. The method, as recited in claim 1, wherein: the first layer is ofSiO₂; the mask is a UV-resist mask; the first process gas comprises amixture of C₄F₈, O₂ and argon and the first plasma etches the layer; andthe second process gas comprises a mixture of CH₃F, argon, andoptionally O₂ and the second plasma forms the polymer deposit on thefeature and the mask.
 9. The method, as recited in claim 1, wherein thefrequency tuning the first RF power source to a first frequency to matchthe first impedance load, and the frequency tuning the first RF powersource to a third frequency to match the second impedance load use amatchbox to partially match the first impedance load and third impedanceload and use frequency tuning to provide a final match of the firstimpedance load and second impedance load.